During neurological or other procedures to the head and neck areas of a patient, it is common for the patient to lie on a table with the patient's head at or extending beyond the end of the table. A head support, designed to hold the patient's head during a surgical procedure, is mounted on a mechanical connector or "base unit" which, in turn, is attached at the end of the table. The base unit has movable elements that permit the head support to be adjusted and clamped at a position and orientation having a desired elevation and longitudinal position with respect to the table. The head support may be a skull clamp which securely and rigidly holds a patient's head in the desired position and orientation. Alternatively, the patient's head may be supported by a head rest, for example, a horseshoe-shaped head rest, or a general purpose head rest.
Typically, the head support is coupled to one end of a swivel adaptor which is an angled connector preferably providing two degrees of rotational freedom. The other end of the swivel adaptor is connected to one end of a swivel arm or transitional arm on the base unit. The transitional arm is used to change the elevation of the head support. A shaft on the other end of the transitional arm is located within a bore at one end of a base clamp. The other end of the base clamp is rotationally coupled to a frame which may be longitudinally and laterally adjusted with respect to the end of the table. Therefore, by rotationally adjusting the transitional arm with respect to the frame, and further adjusting the position of the frame relative to the table, the head support can be moved into any desired position and orientation.
In accordance with a known prior art design illustrated in FIG. 4, the end of the base clamp 10 contains a threaded hole 11, reaching to the bore 12, through which a thumb screw 13 extends. The distal end 14 of the thumb screw 13 is located in an annular groove 15 in a shaft 16 on the other end of the transitional arm 17. Therefore, the distal end 14 of the thumb screw 13 and the annular groove 15 provide a guide for the pivoting action of the transitional arm 17 with respect to the base clamp 10, and further, prevent the transitional arm 17 from separating axially from the base clamp 10. The thumb screw 13 is loosened to disengage it completely from the annular groove 15, thereby permitting the transitional arm 17 to be removed from the base clamp 10, as for cleaning. In addition, the thumb screw 13 itself may be unscrewed from the base clamp 10, so that the thumb screw 13 and its mating hole 11 in the base clamp 10 can be cleaned.
While the above design works satisfactorily, it does have several disadvantages. First, the screw 13 extends from the base clamp and is subject to being inadvertently hit or bumped. Consequently, the screw 13 is subject to being damaged or broken off in the threaded hole 11. Therefore, use of the base clamp is impeded, if not prevented, until the broken screw can be removed and replaced with a new screw. Further, the surfaces of the screw 13 which are outside the base clamp have the further disadvantage of collecting contaminants, and therefore, must be cleaned. When the screw 13 is separated from the base clamp for cleaning, it can be lost which prevents use of the base clamp until the screw is replaced.